Telephone system



E. E. HINRICHSEN TELEPHONE SYSTEM Sept, '27, 1921.

Filed July 26, 1923 3 Sheets-Sheet 1 Sept. 27, 1927.

E. E. HINRICHSEN TELEPHONE SYSTEM Filed July 26, 1923 3 Sheets-Sheet 2 hwy/0 [Zn 4M [Mm/mam Sept 1927' E.- E. HINRICHSEN TELEPHONE SYSTEM M mm m 1 m san wwh W Filed July 26, 1923 Patented Sept. 27, 1927.

UNITED STATES PATENT oFFic-s.

EDWARD- E. HINRICHSEN, OF NEW YORK, 11'. .Y., ASSIGNGR T WESTERN ELECTRIC COMPANY, INCO RIPORATED, OF NEW YORK, NT. Y., A GQBEORATIGN OF NEW YORK.

TELEPHONE SYSTEM.

Application filed July 26,.

This invention relates to telephone systems and particularly to machine switching systems of small capacity, such as those used for private branch exchange working.

' The object of the invention is to provide a simple, flexible and efficient relay type system in which the first cost and the cost of maintenance will be low.

A feature of the invention is the provision of a counting relay selector comprising means responsive to any number of single impulses spaced in time apart from each other to select'a particular line and also responsive both to a series of N impulses and to single impulses spaced in time apart from a sacceeding series of l impulses to select another particular line.

Another feature of the invention resides inmeans for testing a called line by means of two simultaneously established circuits leading through relays which control each other whereby the operation of one will open the circuit of the other. Such an arrangementcontemplates the use of two relays of different time limits and the preferred embodiment of this invention is illustrated in a fast relay responsive to a busy condition and a slow relay responsive to an idle condition. Thus, when a link circuit is extended to a busy called line, the fast relay Will immediately energize and cut off the slow relay and when the link circuit is extended to an idle called line, the slow relay will energize and cut oil the fast relay.

Another feature of this invention resides in the means for immediately disconnecting the link circuit from a called line upon the discovery of a busy condition.

A further feature of the invention resides in the provision of a resistance in series Withthe holding relay of a link circuit. During the dialing period this resistance is short circuited so that the flow of current in the holding relay is increased and such relay is thus rendered slow torelease. After the dialing period the short circuit about the said resistance is removed and the relay thereafter is quick acting. 1

Another feature of this invention consists of means responsive to a series of impulses greater than a predetermined number for switching the calling subseribers line to an operator.

The invention is shown three figures which when. placed with Fig. 1 above Fig. 2

line is idle and the fast relay fails to ener- 1923. Serial No. 653,833.

lay individual to the calling line and individual to the link circuit is energized and the line is extended to the link circuit. The extension of the line to the link circuit causes the energization of a cut-off relay individual to the calling line whereby the'control exercised by the calling line over the line relay is now transferred to the impulse relay of the link circuit. The calling subscriber now manipulates his impulse sender to send a particular number of impulses corresponding to the desired called station. A set of counting relays individual to the link circuit is operated anda relay individual to the called line and individual to the called end of the link circuit is energized, thus extending the link circuit to the called line. A test of the called line is now made by means of completing two circuits, one through a fast relay of the link circuit and another through a slow relay of the link circuit. If the called line is busy, the fast relay becomes operated and opens the circuit of the slow relay. If the called line is idle the circuit of the fast relay will be ineffective and after an interval 90 the slow relay will become energized and open the circuit of the fast relay.

The fast relay controls the ringing tone and the busy tone. Therefore, if the called gize, a small amount of ringing, current will be connected through the armature of the fast I relay to the calling p'artys line, thus ap praisi-ng such calling party of the fact that ringing current is being transmitted to the called line. 1 If on the other hand, called line is busy and the fast relay becomes energized, then the movement of armatures connects a busy tone to the calling subscribers line and he is thereby appraised of the fact that such called line is busy. a

The operation of the fast relay, beside switching bus-y tone on to the calling sub scribers line,. also causes the deenergization of the connecting relay by means of which the link circuit was extended to the called line.

The operation of the counting relays should be especially noted. There is a first set of counting relays whichis normally operated in response to a first impulse. If a second impulse follows immediately, the second set of counting relays is passed by and the third set of counting relays is operated instead.

Thus, a train of two impulses will operate the third set of counting relays. If, on the other hand, the impulse is notimmediately followed by a second impulse, an auxiliary relay will be energized so that if two impulses are now sent, the first will operate the second set of counting relays and the second will operate the third set of counting relays. In this manner, the third set of counting relays is operated either by a train of two impulses or-by two trains, one of a single impulse, and the second of two impulses.

Under ordinary conditions, then, the second set of counting relays is never used for establishing a connection to an ordinary subscribers line. This fact is utilized in the present system by making the called number of the outgoing trunks to the central olfice a particular two digit number, to wit, .11. Thus, the first impulse operates the first set of counting relays and during the interval following the auxiliary relay is energized.

Then, upon the transmission of the second impulse representing the called number 11, the second set of counting relays is operated and such operation results in the establish outer left hand armature of relay 201 to ground. Relay 200 is energized in this circuit and attracts its armatures.

We will assume that the first link circuit indicated in Fig. 2 has been taken for use and that consequently, relay 202 is at this time energized. Therefore, a circuit will be established from ground, outerright armature and front contact of relay 200, conduc tor 203, left hand armature and front contact of relay 202, left hand armature and back contacts of relay 204, and thence in one direction through the winding of relay 205 to battery and ground and in another direction over conductor 206, winding of relay 300, to battery and ground. Relays 205 and 300 become energized in this circuit. Another circuit is now establishedfrom ground, inner right hand armature and front contact of relay 200, conductor 207, front contact and outermost left hand armature of relay 205,

winding of relay 208 to battery and ground.

is now put in connection with the windings of relay 301. Upon the energization of relay 208, alocking circuitis provided from ground, front contact and right hand armature of relay 300, the front contact and inner left hand armature of relay 208, winding of relay 208, to battery and ground. The energization of relay 208 also provides a circuit for the energization of cut-off relay 201 extending from ground, innermost left hand armature and front contact of relay 208, winding of cut-off relay 201 to battery and ground whereupon relay 2 00 becomes dcenergized and opens the circuit for relay205 just described.

Upon the energization of relay 301, a circuit is established from ground, left hand armature and front contact of relay 301, conductor 302, right hand armature and back contact of relay 20.9,normal contacts of the inner right armature of relay 210, winding of relay 210, left hand Winding of relay 204 tobattery and ground. Relay 204 becomes energized in this circuit and looks through its right hand Winding, front contact and inner right hand armature to the ground supplied at the back contact and armature of relay 211, whereupon any further calls will be directed to other link circuits beyond those controlled by relays 202 and 204. Relay 210 becomes energized in series with relay 204 and through its right hand armature establishes a substitute circuit for itself and the left hand Winding of relay 204 through the front contact and left hand armature of relay 300. Upon the energization of relay 210, acircuit is established from ground, front contact and outer ground, the armature and front contact of relay 301, conductor 302, right hand armature and back contact of relay 209-, front contact and outer right hand armature of relay 210, left hand armature and front contact of relay 306, winding of relay- 300 to battery and ground. The connection is now in a stable condition awaiting the sending of impulses from the calling subscribers substation 100. o

The manner in which a preliminary impulse is absorbed will first be described. This preliminary impulse will take the form of a short interruption of the circuit of substation 100 whereupon relay 301 will retract its arn'iature for an instant. At this time, a circuit will be established extending from ground, armature and back contact of relay 301, front contact and inner left hand armature of relay 210, conductor 214, conductor 307, right hand armature and back contact of the last counting relay 308, in series through the right hand armatures and back cont-acts of all other counting relays to the winding of relay 309, and thence to battery and ground. In parallel with relay 309, ground will be extended over conductor 307 to thwinding of relay 310, which relay also becomes energized at this time. Upon the energization of relay 309, a circuit" is extended from ground connected as described to the upper terminal of relay 309, the wind- 'ng of relay 311, the front contact and right and armature of relay 309, back contact and left hand armature of relay 312, the,

back contact and left hand armature of relay313, conductor 314 to the ground connected to the winding of relay 306. Relay 311 is therefore short-circuited at this time and does not become energized. When relay 301 now beomes energized, the ground is removed from conductor 307 and the shortcircuit is therefore removed from relay 311 which at this time becomes energized. Relay 310 is slow to release and hence mainains its armature attracted for a short in terral to await the sending of another impulse. If this first impulse is not followed by another in a short interval, relay 310 will become deenergizcd and close a circuit from ground, the front contact and outer left hand arniiature of relay 210, conductor 213, normal contacts of the left hand armature of relay 30%, right hand winding of relay 315, conductor 316, the armature and back contact of relay 310, armature and back contact of relay 317, conductor 318, front con tact and left hand armature of relay 309,,

winding of relay 319, to battery and ground. Relay 319 becomes energized in this circuit and immediately locks in a circuit including its winding front contact and left hand armature, conductor 3.14, to the ground con-- uected to the winding of relay 306. It will thus be seen that a preliminary impulse results in the energization of relay 319.

Let us now assume that the subscriber at station 100 dials the digit 3 in order to establish a connection to substation 101. By manipulating his substation sender to send the digit 3, the subscriber at station 100 will interrupt the circuit of relay 301 three times in quick succession. The first interruption of this circuit will result in placing ground momentarily on conductor 307 which causes the energization of relay 310 and which is connected in parallel therewith through the right hand armatures and back contacts of the counting relays until it reaches the right hand armature of relay 311, whence it will be extended over the front contact of relay 311, the right hand armature and front contact of relay 319, winding of relay 320 to battery and ground. Relay 320 will become energized'in this circuit and establish a circuit for relay 31-2which, however, is ineffective until the ground is disconnected from conductor 307. Upon the attraction of the armature of relay 301, relay 312 becomes energized and prepares a circuit for the energization of relay 321. Upon the next interruption of the calling subscribers line circuit, a ground will be extended over conductor 307, thence over the right hand mature and front contact of relay 312, Wind ing of relay 321, to battery and ground. Relay 321 becomes energized and establishes a circuit for relay 313 which is ineffective at this time. Upon the attraction of the armature of relay 301, relay 313 becomes energized. Upon the last retraction of the armature of relay 301, a ground is extended rom conductor 30?, the right hand armature and front Contact of relay 313, winding of relay 322, to battery and ground. Relay 322 becomes energized and establishes a circuit for relay .323 which becomes effective upon the attraction of the armature of relay 301. This being the final impulse, none other of the counting relays are now ener ized and after a short interval, relay 310 becomes deenergized, whereupon a circuit is established from ground, the front contact and outer left hand armature of relay 210, conductor 213, normal contacts of the left hand armature of relay 30%, right hand winding of relay 315, conductor 316, armature and back contact of relay 310, armature and back contact of relay 317, conductor 318, front contact and left hand'armature of relay 322, conductor winding of relay 215, to battery and ground. Relay 21.5 becomes energized in this circuit and looks through its front contact and right hand armature, conductor 216, winding of relay 305, to the ground supplied over the normal contacts of the left hand armature of relay 304. As long as the original energizing circuit of relay 215 is maintained, relay 305 is short-circuited and does not attract its armatures. The testing and ringing connections which now take place will be described in detail somewhat further on.

To simplify the drawings five p rs of counting relays are omitted bet veen the pair of relays 322, 323 and the pair 308, 350. The left-hand armature of each of the omitted relays and of relay 350 would be connected to relays such as 215 in the same manner as the left-hand armature of relay 322 is connected to relay 215. Thus, any one of nine subscribers may be called in the manner above described.

It has now been shown how the substation 101 my be selected through the energization of relay 215by sending three impulses after the preliminary impulse has been sent. It will now be shown how substation 101 may be selected by sending three impulses in the first place without a preliminary impulse. Upon the first deenergization of relay 301, a ground is placed on conductor 307 which energizes relay 310 and in parallel therewith extends-through the right hand armatures and back contacts of all of the counting relays to the winding of relay 309 and thence to battery and ground so that relays 309 and 310 now become energized. Relay 309 establishes a potential circuit for relay 311 in the manner hereinbefore described. Upon the subsequent attraction of the armature of relay 301, relay 311 becomes energized. Since this impulse is now fol." lowed by another impulse grounding conductor 307 before relay 310 can become energized, the ground now placed on the right hand armature of relay 311 is extended tlirough the right hand armature and back contact of relay 319 and thence through the winding of relay 321 to battery and ground. In this manner, the pair of counting relays 312 and 320 is skipped. Thus relay 321 becomes energized on the sending of the second impulse and relay 313 becomes energized at the end of the second impulse. Relay 322 becomes energized upon the sending of the third impulse and relay 323 becomes energized upon the end of the third impulse. In this manner, conductor 324; will again be connected to ground in the manner hereinbefore described and relay 215 will become energized. Since the circuit for ,relav 215 also extends throu h the ri 'ht hand winding of relay 315, this relay will become energized. A circuit -is now established from battery, winding of relay 325, left hand winding of relay 315, front contact and left hand armature of relay 315,

armature and back contact ofrelay 326, through thenormal contacts at left hand armature of relay 304:, and thence to ground at the front contact and left hand armature of relay 210. Relay 315 becomes locked in this circuit and relay 325 becomes energized.

The energizatiim of relay 325 starts the ringii'ig relays into action. These ringing relays are arranged in three groups of two relays each, each group forming an interrupting means. Thus, relays 326 and 327 form one group which constitute a slow acting interrupter. Relays 323 and 329 form a second group which constitute a fast acting interrupter, and relays 330 and 331 form a third group which constitute a very slow interrupter. The first two groups are self acting and the third group comprising relays 330 and 331 are dependent upon the actionofthe first group of relays 326'and The action of the tirst group is as follows: ground is extended to conductor 332, over/the front contact and armature of relay 325. This ground extends through the armature and back contact of relay 327 winding of relay 326 to battery and ground. Relay 326 attracts its armature and extends ground from conductor over the armature and front contact of relay 326, winding of relay 327 to battery and ground. Relay 327 in attracting its armature opens the original energizing circuit of relay 326 which after an interval, measured by'its slow releasing adjustment, becomes deenergized. Upon the deenergization of relay 326, the circuit of relay 3n7 is opened. and after another interval measurcd by the slow releasing adjustment of relay 327 this relay becomes deenergized, whereupon relay 326 again energizes and the cycle just described is repeated. Upon each energization of relay 327, the ground 011 conductor 332 is extended over the armature and front contact of relzy 327 to the left hand armature of relay 330. Upon the first connection of ground over the front contact of relay 327 a circuit is established over the left hand armature and back contact of relay 330, winding of relay 331, back contact and right hand armaturefof relay 330 to battery and ground. Relay 331 becomes energized in this circuit. Through the front contact and left hand armature of relay 331, the ground supplied to thewinding of this relay is extended to the left hand winding of relay 330, but since the other terminal of the left hand Winding of relay 330 is connected to conductor 332, relay 330 does not become energized at this time. Upon the decnergization of relay 327, a circuit is established from ground on conductor 332, left hand winding of relay 330, left hand armature and front contact of relay 331, winding of relay 331, back contact and right hand armature of relay 330, to batteryand ground. Relay 330 be comes energized in this circuit and by attracting its arinatures opens the original energizing circuit of relay 331 but this relay now remains energized in a circuit extending through the left hand winding of relay 330, left hand arn'iature and front con tact of relay 331, Winding of relay 331, right hand winding of relay 330,to battery and ground. Upon the next energization of relay 327, ground is extended from conductor 332, the left hand armature and front contact of relay 327, the left hand armature and front contact of relay 330, the right hand winding of relay330 to battery and ground.

fit

This action by placing a ground on the right hand terminal. of relay 331 short-circuits this relay and it becomes deenergized. Relay 330,11owcver, remains energised in this it just des- Upon the next deenergization of relay 327, ground is removed from the left hand armature of relay 330 and this relay now becomes decnergized.

It should be noted that for two cycles of operations of relay 32?, relays 330 and 331 go through a single ycie of operations. It should be further noted that during a certain period of the cycle of operation of relays 330 and 331, that is, during the simultaneous energization of both of these relays a circuit is established from battery, right hand armature and front contact of relay 330, front contact and right hand armature of relay 33;, to conductor Thus hat s, at certain intervals, connected to the e point of the primary winding of transformer 334.

During the operation of the two pair of interruption relays just described, the pair comprising relays 328 and 329 forming the operating interrupter are operated as f llows: The ground on conductor 332 is eX. tended over the inner left hand armature and hack contact of relay 329, winding of relay resistance 335 tobattery and ground. Relay becomes energized in this circuit d extends a connection from ground on conductor 332, the outer right hand armature and front contact of relay 328, winding of relay 329, resistance 336 to battery and ground. Relay attracts its armatures nd thereby opens the original ener izing circuit of relay 328. Relay 328 is now shortcircuited by the outer left hand armature of relay 329, such circuit extending from the outer armature of relay/ 329, the front contact .ssociated therewith, the lower terminal of relay 328, the winding of relay 328, resistance 337, the front contact and inner right hand armature of relay 328 to the outer left hand armature of relay 329. Relay 328 now becomes deenergized and in a manner similar to that hereinbefore described, opens the original energizing circuit of relay 329 and at the same time short-circuits it through the outer right hand armature and back contact of relay 328. Relay 329 now becomes deenergized thus completing the last act of the cycle of operations of relays 328 and 329. Since these two relays are fast operating, heir action will be rapid. The function of this setof interrupting relays is to switch a ground connection first from the right hand and then the left hand primary windings of the transformer 334. The flow of direct current first through the right hand primary winding of the transformer and then through the left hand primary winding of the transformer create-s in the. secondary winding the alternating current of ringing frequency, which is transmitted over the conductors 339 and 340 to the points in the link circuits where ringing current is supplied. Since the flowof direct current in the primary windings of transformer 334 is controlled at the, righthand armature of relay 331, there will be an interrupted flow of ringing current in the secondary circuit thus providing what are known as the ringing and the silent intervals. During the silent intervals the battery in series with the secondary windingof transformer 334 pro vides means forenergizing the ringing cutoff relay 326.

Going back now to the point where the connecting relay 215 was energized, it will be noted that a circuit is established from the winding of relay 215 which extends in one direction over conductor 324, the left-hand armature and front contact of relay 322, conductor 313, back contact and right hand armature of relay 317, the contact and ar mature of relay 310, the right-hand Windingof relay 315, the normal contacts of the left-hand armature of relay 304 to ground supplied at the armature and back contact ofrelay I 210 and in the other direction through the front contact and right-hand armature of relay 215,'conductor 216, winding of relay 305, normal contacts of the left-hand armature of relay 304 to the same ground supplied at the left-hand armature and front contact of relay 210. Thus, the winding of relay 305 and the right-hand winding of relay 315 are included in parallel. At the same time a circuit is established from battery, the right hand winding of relay 304, the back contact and right-hand armature of relay 305, conductor 341, the inner left-hand armature of relay 215, winding of cut-offrelay 217 to battery and ground. If the called line is idle, this latter circu twill be ineffective, since battery is opposed to battery. If, on the other hand, the called lineis busy, then a ground connection will be found on the front contact and innermost left-hand armature of relay 215 and relay 304 will be energized in this circuit. Relay 305 is adjusted to be slightly slow in operatin so that the circuit just described for it is not effective to open the circuit for relay 304 in case the line is busy and the operation of relay 304 will thereupon open the circuit for relay 305. If, on the other hand, the line is idle, the circuit for relay 304 is ineffective and the circuit for relay 305 becomes eflective so that relay 305 attracts its armatures in a short interval and opens the circuit for the right-hand winding of relay 304 and substitutes a ground connection on the test conductor which results in the energization of the cutoff relay 217. The operation of relay 305 under these conditions, removes the ground from conductor 314 resulting 1n the deener gization of relay 306- and the counting relays which have been energized up to this point. Upon the deenergization of relay 306, resistance 303 is included in the circuit of relay 300 which, during the dialing period was required to be slow in releasing. Hereafter during the connection this slow releasing feature is not needed in relay 300 so that resistance 303 may be introduced to limit the flow of current during the talking period. It will'be understood that limiting the flow of current in this relay int-his manner renders it fast to release.

The deenergization of relay 306 also operatesto connect ringingcurrent to the called line, the circuit for which may be traced from ground, at the secondary of transformer 334, conductor 339, the front contact and innermost right-hand armature of relay 315, the back contact and inner right armature of relay 306, the outermost left-hand armature and front contact of relay 215, through the ringer at substation 101 and back over the front contact and middle left-hand arma ture of relay 215, outer right-hand armature and back contact of relay 306, outer righthand armature and front contact of relay 315, winding of relay 326, conductor 340, the secondary winding of the ringing transformer 334 to battery and ground. The current flowing over this circuit intermittently rings the bell of the called substation 101.

During the ringing of the called line, a small amount of ringing current is transmitted from conductor 340, winding of relay.

326, front contact and outer right-hand armature of relay 315, conductor 342, back contact and right-hand armature of relay 304, condenser 343, left-hand winding of relay 344 to ground. Through induction, this ringing current is transmitted as a ringing tone to the calling subscriber to appraise him that the called line is being rung. hen, in answer to the summons of his bell, the called subscriber removes his receiver from his hook, the current traversing the winding of relay 326 is increased to an amount sufficient to energize this relay, whereupon the holding circuit for relay 315 is broken and this relay becomes deenergized, thus connecting the windings of relay 344 to the called subscribcrs line. Talking current is now supplied to the called subscriber through the windings of relay 344 and it becomes energized. Through the armature and contact of relay 344 a ground connection is made to the winding of relay 210 so that this relay with the left'hand winding of relay 204 in series therewith is now under the joint control of both the calling and called subscrib ers. Should the calling subscriber hang up first and thereby release relay 301, relay 300 will become released. The deenergization of relay 300 opens the holding circuit of relay 208 so that this relay now becomes deenergized and renders the calling line free. WVhen, subsequently, the called subscriber re places his receiver on its hook, relay 344 becomes deenergized, thus opening the circuits of relays 210 and 204. The deenergization of these two relays opens the holding circuit of relay'215 and renders both the called line and the link circuit free for further use.

Returning now to the point where the called line is found busy, it will be remembered that relay 304 becomes operated. Relay 304 thereupon opens the circuit of relay 305 and locks itself in a holding circuit including battery and ground, the left winding of relay 345, left hand winding of relay 304, the left-hand armature and alternate contact of relay 304 to ground at the outer left-hand armature and front contact of re lay 210. Relay 345 becomes energized in this circuit and closes a circuit for buzzer relay 346. This circuit may be traced from ground, the armature and contact of relay 345, back contact and armature of relay 346 to battery and ground. In parallel with the contact and armature of relay 346, there is a resistance 34'! designed to reduce the spark at the contact to a minimum but still insufficient to hold relay 346' energized after it has at tracted its armature. Relay346 being in a self-interrupting circuit vibrates its armature and thereby rapidly raises and lowers the potential on conductor 348 producing a tone which is transmitted through the front contact and right-hand armature of relay 304, condenser 343, the left-hand winding of relay 344 to ground. This tone is transmitted by induction to the calling subscriber to appraise him that the called line is busy.

The operation of relay 304 besides removing the ground connection to the 1 left-hand terminal of relay 305, also opens the holding circuit of ringing relay 315, the circuit of relay 306, the circuit of the counting relays now operated, a'nd the circuit of relay 215, whereupon these relays become deenergized, leaving the calling subscriber in control of the link circuit with busy tone being transmitted to his substation. lVhen he replaceshis receiver on its hook relay 301 becomes deenergized and releases the connection as hereinbefore described. A trunk to the central oliice is selected by sending two trains of impulses containing one impulse each, which corresponds to the designation 11. The first impulse operates the counting relays 309 and 311 in the same manner as described in connection with the preliminary impulse. The second impulse, which does not follow until after relay 310 has become energized, now causes the energization of counting relays 312 and 320, as described in connection with the first impulse in the train sent after apreliminary impulse had been recorded. The energization of relay 320 is followed by an interval, after which lli) 316, arn nine and back relay 310 becomes deenergized a second time and a circuit is established from ground, the front contact and outer left armature of relay 210, conductor 213, the normal contacts of the left hand armature of relay 30 1, right hand winding. of relay 315, conductor contact of relay 310, right hand armature and back contact of relay 317, conductor 313, front contact and left hand armature of relay 320, conductor 34 :5, winding; 0f relay 209 to battery and ground. Relay 209 attracts its armatures and establishes a circuit from ground, armature and front contact of relay 301, right hand armature and front contact of relay 209, conductor 212, left hand armature and front contact of relay 102, which we will assume to be crgized this time, left hand armature and back contacts of relay 104, winding of relay 105 to battery and ground. A circuit is also established from ground, the outermost left hand armature and front contact of relay 200. the outermost right hand armature and front contact of relay S, conductor 218, innermostleft hand armature and front contact of relay 105, relay 103 to battery and ground. Relay 108 locks up to a ground which will be connected to conductor 103 in response to the seizure of the trunk circuit controlled by relay 103. The cnergization of relay 209 results in the removal of the ground connection to the windings of re 210 and 204:, whereupon these relays become deenerg .ed. It willbe remembered that a ground was extended frnin the armature and front contact of relay 301, thr. ugh the right lud armat re and back contact of relay 200, the front contact and outermost right hand armature of relay 210, the left hand armature and front contact of relay 306, winding of relay 300 to battery and ground. Upon the movementof the right hand armature of relay 210 this circuitis opened and relay 300 becomes dcenergized. The retrac- 'tion of its air-matures by relay 300 opens the holding circuit of relays 210 and 20 1, whereupon these relays become deenergized. The deenergization of relay 300 at the same time opens the holding circuit of relay 203 so that this relay now retracts its armatures and restores the link circuit to its normal condition.

Since the operation of the trunk circuit is similar to that disclosed in the Patent No. 1,567,054, issued Dec. 29, 1925 to Edward E. l-Iinrichsen, no further description thereof will be given.

It should be noted that if all of the trunk advance relays, such as 102 and 104, are operated, then a circuit will be established from the ground on conductor 212, over the left hand armatures and front contacts of relays 102, 10%, etc., conductor 106, the front contact and innermost left hand armature of relay 209, left hand winding of relay 1,

winding of relay 345, to battery and ground. Relays 304 and 3 15 become energized in this circuit and cause th transmission of busy tone to the calling subscriber in the manner hereinbefore described,.:and upon the r" lacing of the receiver at the calling substation, the link circuit and other apparatus is restored to normal.

Let us assume tiat station. 107 is used by the attend t subscriber. Since it is the usual practice to reach the attendant subscriber or operator by dialing zero, we will assume that a pair of counting relays 308 and 350 control the connection to the ninth subscribcfis line. Therefore, when zero is dialed, relay 308 will be energized upon the end of the ninth impulse. Upon the beginning of the 10th impulse a circuit will be established from ground on conductor 307, through the right-hand armature and front contact of relay 308, the normal contact of the lefthand armature of relay 317, win-ding cf relay 317, to battery and ground, whereupon this relay will attract its armatures.

It will be noted that upon the energizat-ion of relay 317, relays 308 ant 350 do not become deenergized as in the case, for instance, where relay 308 is energized, thus releasing relays 323 and 322. However, since the right-hand armature of relay 317, controls the connection through conductor 313, the continued energization of relays 303' and 350 is ineffective. A short interval after the tenth impulse has been sent, relay 310 be-' lot) it Join the tenth im ulse and onened its ori 'i- .nal energizing circuit and locked to the ground on conductor 314. Therefore means are provided whereby every call will be antomatically directed to the attendant subscriber when the calling subscriber sends more than a given number of impulses.

What is claimed is:

1. Ina telephone system, subsc 'ibers lines, a link circuit, impulse sending means for operating said link circuit for interconnecting said lines, a busy test arrangement comprising a fast operating relay and a slow operating relay, circuits completed for both said relays when said link circuit is extended to a busy line, and means controlled by the energization of said fast operating relay for rendering the circuit of said slow operating relay ineffective so as to prevent the opera tion of said slow relay.

2. In a telephone system,subscribers lines, a link circuit, impulse sending means for controlling said link circuit to interconnect said lines, a busy test arrangement comprising a fast operating relay responsive to a busy condition and a slow operating relay responsive to an idle condition, mutually dependent circuits completed for said relays when said link circuit is extended to one of said lines whereby the operation of either of said relays renders the circuit of the other inciiective. V

In a telephone system, subscribers lines, a link circuit tor interconnecting said lines, impulse sending mcansfor controlling said link circuit, a busy test arrangement comprising a relay responsive to a busy condition and a relay responsive to an idlecondition, mutually dependent circuits completed for said relays when said link circuit is extended to one of said lines whereby the operation of either of said relays renders the circuit of the other inettective.

4t. In a telephone system, subscribers lines,

q a link circuit for interconnecting said lines,

relays for connecting said lines to said link,

selectively controlled relays for connecting said link to said lines, a pair of test relays, mutually dependent circuits for said relays established upon the operation oi? one of said selectively controlled relays, the operation of either of said test relays rendering ineii'ective the circuit of the other, a source of ringing tone and a source of busy tone associated with one oi said test relays, means responsive to the operation or. said one of said test relays for deenergizing the said operated selectively controlled relay and transmitting busy tone to the calling subscriber, and means responsive to the operation 01' the other of said test relays for transmitting ringing tone to the calling subscriber.

In a telephone system, a link circuit, a line relay associated with said link circuit responsive to separate impulses of a train of impulses, a relay controlled by said line relay, a circuit for said last relay, a resistance in said circuit, and means for short circuiting said resistance during the transmission of a train of impulses to said line relayto render said last relay slow acting at such time only. j

6. In a telephone system, a selector comprising a plurality of counting relays responsive to a plurality of time spaced single impulses for selecting a particular line and responsive both to a series of Nimpulses and to a single impulse spaced in time lQGfOIG a series of N impulses for selecting another particular line.

7. In a telephone system. a prisinga plurality of sets of counting relays, auxiliary relay for normally rendering a particular set inoperative, and means responsive to a single impulse tor energizing selector eomsaid auxiliary relay to render said particular set of counting relays operative.

8. In a telephone system, a plurality of counting relays, means responslve to a tram ot' a definite number of impulses for eneror by sending first a train of one impulse andthen a train of two impulses, and means for energizing said second set of relays sending two separate trains of one impulse each.

10. In a telephone system, a calling line, a plurality of called lines, an attendants line, link circuits, each having a separate set of contacts for making connection with each of said lines, means responsive to a call on saidcalling line for operating said contacts to connect the calling line to one or said link circuits, digit control means for operating the contacts of the respective called lines to connect said link circuit to any called line according to the digit representing such line, and means controlled in accordance with a plurality of different digits for operating the contact-s individual to the attendants line for connecting a link thereto.

In witness whereof, I hereunto subscribe my name this 23rd day of July, A. D. 1928.

ED'W'ARD E; HINRICI-ISEN. 

